The present invention relates to a method for coating a press or transfer belt, in which a coat is formed on the surface of the belt comprising one or several polymers and possible blend components and additives. The invention also relates to a corresponding coated belt. In particular, the invention relates to press or transfer belts in a paper machine.
Various kinds of press and transfer belts used in a paper machine are known from paper publications EP 509 460 (Yamauchi Corp.), EP 786 550 (Conrad Munzinger and Cie. AG), EP 576115 (Albany International), and WO 95/34715. Generally, a belt of this type comprises a woven supporting structure and a polyurethane matrix. The seam in the belt is often a nuisance in papermaking. In the first publication referred to, the seam is avoided by means of a construction, in which a narrow strip soaked in polyurethane elastomer runs in an endless spiral to form a belt without a transverse seam. In belts with transverse seams, the effect of the seam becomes emphasized or appears as the belt wears.
The present invention is intended to create a method for coating a press or transfer belt and creating a coated belt, by means of which the life of the belt can be lengthened and/or its characteristics improved. By means of the invention a coating is applied to the surface of a worn, scratched and/or otherwise damaged belt to restore its characteristics, or if it is wished to provide the belt with new surface characteristics.
The optimal properties for a belt in different applications are achieved through the selection of different materials. The relevant properties are hardness, density, and filler contents. From the point of view of a long service life, the most important characteristics of these properties are their homogeneity and especially their profiles in all directions, i.e. in the x, y, and z directions. With the aid of the invention, the belt is always seamless, which characteristic is retained even when the belt becomes thinner through wear.
According to one preferred embodiment of the invention, the basic polymer chains of one or more components of the coating are modified with halogenated macro-oligomers, diols, triols, thiols and/or other polyols. In the most preferable modification the halogen used is fluor, but iodine or bromine may also be used. Halogen treatment of this kind, in which the basic polymer of the coating itself is modified, is considerably more effective that the traditional treatment of the surface with a substance containing halogen particles.
The coating of a belt is intended to restore the original good characteristics of the belt or to improve the characteristics of the belt in its current application. The homogeneity of the coating is a particularly important property.
The invention is next described with reference to the accompanying figures, which illustrate some embodiments of the invention.